This invention relates to improved well instruments for indicating or responding to changes in the inclination of a well.
In steering tools for directional drilling and in well surveying equipment, it is often desirable to utilize an instrument or tool which is lowered into a well and produces an indication or record of, or otherwise responds to, the inclination of the well and the direction of that inclination. The probe which is lowered into the well usually includes gravity actuated sensors which respond to changes in inclination relative to the true vertical, and direction responsive sensors such as magnetically actuated flux gates.
Over a period of time, instruments of this type may develop offsets or inaccuracies in the sensing means or other related elements, resulting in the introduction of corresponding errors into the readouts produced by the equipment. Such offsets may occur or vary at any time during the life of the instrument, and are completely unpredictable and very difficult to detect and measure.